Telephone system



Dec. 30, 1.941.

s. s. MCANDREW TELEPHONE SYSTEM FiledV June s, 1940 9l Sheets-Sheet l I .ILIL

xNvENToR SMART S. MC ANDREW BY. ,XM1/.1:7

M iM Mm ATTORNEYS Dec. 3o, 3941.

Filed Jung 8, 1940 9 Sheets-Sheet 2 1 i CENTRAL 00 OF F /C E f ff I D/STANT I EXCHANGE J. B. X. 40

OPE R F/NDER CON/VEC TOR CIRCUIT' F/G. l0 FIG.

INVENTOR SMART s, Mc ANDREW ATTORNEYS Dec. 30, 1941. s, s, MCANDREW 2,268,047

TELEPHONE SYSTEM Filed June 8, 1940 V9 Sheets-Sheet 3 ATTORNEYS Dec. 30, 1

5 @Zi l m4 S. S'. MCANDREW TELEPHONE SYSTEM 9 Sheets-Sheet 4 Filed June 8, 1940 De.\v 30, 1941.

FINDER 700 s. S. MCANDREW TELEPHONE SYSTEM Filed June 8, 1940 sw/rcH L/NK soo l 9 Sheets-Sheet 6 SELE C TUR 520 adm,

INVENTOR SMART S. MO ANDREW ATTORNEYS Filed June 8, 1940 9 Sheets-Sheet 7 www# SMART s. Mc ANDREW ATTORNEYS Dec. 3o, 1941.

S. S. MCANDREW TELEPHONE SYSTEM.

Filed June e, 1940 9 sheets-sheet 9 I (Ll. J L

rC/080 r C4 6 8 F/Rsr P05/NoN APPAPA m5 //00 SMART S. MC ANDREW ATTORNEYS Patented Dec. 30, 1941 f azsacir TELEPHONE sYsTEM l Smart S. McAndrew, Barranquilla, Colombia", as-

signor to Associated `Electric Laboratories, Inc., Chicago, Ill., a corporationof Delaware Applicativi, June s, 194o,fser`ia`1 No. 339,475

` The presentl invention relates to telephone sys-- tems and more particularly to improved auto- `matic` switching apparatus of the character of thatdisclosed and claimed in U. S. Patent No. 2,070,874`-John H. Voss and Thomas F. Crocker, issued February 16, 1937, which apparatus is connected and arranged to handle switchboard trafi'ic.

,A telephone system of the character'of that disclosed in the Voss and Crocker patent mentioned Vcomprises a switchboard provided with a number of operator positions and a number of groups of switching links individually associated with the operator positions, each operator position ."comprising equipment operative to select any, idle one of the switching links in the associated group of switching links. Each switching link includes an answer switch and a call switch, the `answer switchof a selected switching link being operativeto. select a calling toll or trunk line accessible thereto and the call switch of a selected switching link being operative to select a called toll ortrunk line accessible thereto. The

operation of the answer switch of a selected.

switching link is controlled automatically by a distributor `commonly associated with the groups of switching links; while thel operation of the,

callswitch ofa selected switching link is under the control of the position equipment at the associated operator position.

. While switching apparatus of `the character .noted is entirely satisfactory in operation and "f ina `,telephone system including an operator sition having switching apparatus associated therewith, an arrangement selectivelyrcontrollable from the operator position for governing the ,L operationof the switching apparatus to select lines accessible thereto, whereby calls on` lines in any given group of lines rendered aparticular class of service may be answered at the operator position in preference ,to calls on lines in another group `of lines rendered a different class of service.

'ssl

at a relatively small switchboard, it is frequently desirable to answer a call on a given line or on lines in a given class of lines in preference `to a callon another line or on linesin another class of lines. p

Accordingly, it is an object of the presentinvention to provide in a telephone system including an operator position having switching apparatus associated therewith, an arrangement selectively controllable from the operator positionfor` governing the operation of the switching apparatus to select lines accessible thereto, whereby a call on any particular one of the, lines in a given group of lines may be answered at the operator position inpreference to a call on` another line in the given group of lines.

Anotherobieci of the invention is to provide in a telephone system` including an operatory position having an automatic switch associated vitherewith, an arrangement selectively controllable from the operator position for governing the operation of the switch in order to cause the switch to select a calling line in Vany particular.

` inv atelephone system including an operator position having `a switching link associated therewith, wherein the switching link comprises an,

answer switch and'. a call switch, improved equipment `at the operator position selectively controllable for ,governing the operation of both the answer switch and the callswitch of the switching link, whereby calls may belanswered by way of the answer switch and extended byway of the call switch of the switching link and delayed calls may bel set up by way of both the answer switch and the call switch of the switching link in an improved and` eicient manner.

A further object of the invention is to provide in a telephone system including an operator posigtion, a combination answer and call switch associated with the operator positionrand an improved arrangement selectively controllable from the operator position for governing the 'operation of the switch as an answer switch or as a call switch.

A further object of the invention is to provide 'in a telephone system including a plurality of operator' positions and a plurality of automatic switches individually associated with the operator positions and equipment at each operator k position `for selectively governing the operation of the associated switch to answer calls on lines accessible thereto, improved apparatus` `corn- Another object of the invention is to provide551the lines accessible thereto.

, of groups of switching links individually asso'- ciated with the operator positions, eachswitching link including ananswer switch and a call switch, theanswerr switchand the call switch' of each switching link having access to trunk` lines and toll `lines interconnecting `the central oiiice, the I. B. X and the distant exchange with the P. A. B. X.

In accordance with one feature of the invention the telephone system comprises a plurality of first. groups of lines, a second group of lines, an operator position, an automatic switch associated with the operator position and having access to the lines, means controlled by the presence of a calling linel in any one of the lrst groups of lines `for transmitting a signal to the operator position identifying the one group of lines, and

additional means controlled by the presence of a call on any one of the lines in the second group of lines for transmitting a signal to the operator position identifying the one line in the second group of lines. Also the system comprises means selectively controllable from the operator position for causing the switch to select a calling line in any particular one of the first groups of lines or any particular calling one of the lines in thersecond group of lines, thereby to extend the call Y on the first-mentioned line or the second-mentioned line by way of `the switch to thel operator position tor be answered. More particularly, the position equipment at the operator position comprisesa plurality of group line keys individually corresponding to the first groups of lines anda plurality of individual line keys. individually conresponding to the lines in the second group of lines, a givengroup line keybeingl operative to cause the switch to select a calling line in the corresponding rst group of lines andagiven individual line key being operative to cause the switch to select thecorresponding calling vline in the second group of lines. Further it is noted that the various rstjgroups of lines and the second group of lines comprise lines which are rendered different classes of service, whereby calls on lines rendered anygiven class of service may be answered at the operatorposition in preference to calls on lines rendered a different class of service.

In accordance with another feature of the inventionthe telephone system comprises a switching` link l'associated with the operator position and including an answer switch and a call switch, the answer switch having access to the first groups.` of lines and the second group of lines and the; call Aswitch having access to another group of lines, means selectively controllable from the operator position for causing the answer switch to select an idle line in any particular one ofthe 'rstgroups of lines or any particular one ofthe lines in the second group of lines, thereby to extend ya delayed call in one direction from the-operatorposition byjway of the answer switch overv the first-mentioned line or the secondmentioned line, and means controllable from the operator position for causing the call switch to select a line in the other group of lines, thereby to extend the delayed call in the other direction from the operator position by Way of the call switch over the last-mentioned line.

In accordance with a further feature of the invention the telephone system comprises a plurality of lines, a plurality of operator positions, a plurality of automatic switches individually associated with the operator positions and having access to the linesfmeans selectively controllable from each of the operator positions for causing the associated switch to operate and select any particular one of the lines, thereby to complete a connection between the operator position and the last-mentioned line, and means controlled while one of the switches is operating to select a given line for preventing operation ofV the other of the switches to select the given line.

In accordance witha further `feature of the invention the 'telephone system comprises a plurality of. two-way lines, an operator position, an automatic switch .associated with the operator position and having access to the lines, the switch being operative as an answer switch to seize a calling one of the lines, thereby to route a call on the last-mentioned line by way of the switch, to the operator position to be answered, the switchbeing operative as a callswitch to seize a calledv one of the lines, thereby to route a. call fromthe operator position by way of the switch to the last-mentioned line, and means controllable 4from the operator position for selectively operating the switch as an answer switch or as a call switch and toV seize any particular one of the lines.

and. additional operating features are attained. The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims.v The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the. following specication taken in connection with the accompanying drawings in which Figure 1 illustrates the general arrangement of a telephone system embodying the present invention; Figs. 2 to .11, inclusive, taken together, illustrate the details of a system having incorporated therein the` features of the invention, as briefly outlined above; and Fig. '12, illustrates the mode of combining Figs. 2 to 11, inclusive, to form a unied system.

Description of the apparatus incorporated in` the 'telephone system trated comprises a central olce 20, a P. A. B. X

30, an I.' B.y X'l and a distant exchange 50. The

central office 20 and the distant exchange 50 are of any well-known type',v each serving a'number of subscriber substations not shown; while the P; A.,B. X and the I. B. X 4i! are of the automatic type, each serving a number of automatic subscriber 'substations More particularly, the P. A. B. X 30 serves a number of subscriber substations, including the subscriber substations T3 and T4; while the I. B. X 40 serves a numberjof gisubscriber substations,` including the subscriber Substations Tl and T2.` The central office' 20 and the P. A. B.X 30 are interconnected by a. group of one-way trunk lines, including the trunk line 205, extending from the central office 20 to theP. A. B. X 30, and a group'of one-way trunk lines, including the trunk line 200, extending from the P. A. B. X 30 to the central oilice 20. The I. B. X 40 and the P. A. B. X 30 are interconnected by a group of two-way trunk lines, including the trunk line 2|0, extending therebetween; while the distant exchange 50 and the P. YAJB. X 30 are interconnected by a group of two-way toll lines, including the toll line 2|5, extending therebetween.

x The central oflice 20, the LB. X 40 and the l distant exchange 50 respectively `comprise an operator position 240, an operator position 260, and atoll operator position 250; `while the P. A. B. X

trunk line circuit 300. Similarly, each trunk line inthe group oftrunk lines extending from the P; A. B. X to thecentral oflice 20 terminates in an outgoing trunkline circuit in the P. A. B. `X 30 and 4at the operator position 2=f||l.in` the central oiiice 20, the trunk line 200 terminating in the outgoing trunk line circuit 350 and at the operator position 240. Also, each trunk line in the group of trunk lines extending between the I. B. X and the P. A. B. X 30 terminates in `a trunk line circuit in the P. A. B. X 30, and at the operator position 26,0 in the I. B, X 40, the

trunk line 2|0 terminating in the trunk line vcircuit 400 and at the operator position 260.1 Finally, each` toll line in the group of toll lines extending between the distant exchange and the P. A. B. X 30 terminates at the operator posi-` tion 250 in the distant exchange 50 and in a toll line circuit in the P. A..B. `X 30, the toll line 2|5 terminating at the operator position 250 and in the `toll line -circuit 500. i

The I. B. X` 40 is provided with a` switch train comprising a number of finder-connector links, including the iinder-connectorlink 230. Also, a

, telephone line having a line circuit individually associated therewith extends to each of the subscriber substations in the I. B. X 40, the telephone lines 220 and 225 respectively extending to the subscriber substations T| and T2` andhaving the line cir-cuits 22| and 226 respectively associated therewith. Finally, a number of trunk circuits are provided in the I. B. X I0-Which are individually associated with trunks terminating at the operator position 260 in the I. B. X 40, the trunk `circuit 230 `being individuallyY associated nector link in the I. B. X 40 has `access to each telephone line `therein and'to each trunk terminating at the operator position 26|).`

The P. A. B. X 30 is provided with alocal switch train comprising a number of` local finderselector links, including the local linden-selector 1ink940, and a number of local connectors, in-

cluding the local connector 94|. Also, telephoner lines having line circuits individually associated therewith extend to each subscriber substation in i theP. A. B. X 30, the telephone lines 930 and 935 respectively extending to the subscriber :substations T3 and T4 and having the line circuits 93| and 936 respectively associated therewith. A number of trunks circuits, including the trunk circuit 600, is provided in the P. A. B. X 30. It

is noted that each of the local finder-selector` links has access to each telephone line in the P. A. B. X 30, to each local connectorand to a number` of trunks individually extending to the `trunk `circuits,lthe trunk 680 individually extending to the trunk circuit 600. i

Further `the P. A. B. X 30 provided with a toll switch train comprising a number of groups offswitchinglinks `individually associated with the operatorpositions, one of the groups, including the switching links 800 and 902, being individually associated with the viirst operator position 900, and another of the groups, including the switching links SI2 and 9|0, being lindi-- vidually associated with the last` operator position 9|0. Each of the switching links comprises a finder and a selector, the switching links 800, 902, SI2 and SIG respectively comprising the nders100, 903, 0|3and3l'l and the selectors 820, 904, 9|4 and 9|8. Also it is noted that each of the switching links in the group, including the switching links 800 and 902, is commonly associated With a cable `extending to the iirst operator position 900; While each of the switching links in the group, including the switching links 0 |2 and 9|6, is commonly associated witha cable 9|| extending yto .the` last operator position 9I0.A

. It is noted that each of the finders has access to a group of trunks individually extending to thegroup of outgoing trunk line circuits, this group including the trunk 305 ,extending to the outgoing trunk line circuit 350; to a group of trunks indivdually extending to the group of inwith the trunk 235 terminating at the operator vposition 260. It is noted thatieach finder-concoming trunk linecircuits, this group including the trunk 350 extending` to the` incoming trunk line circuit 300; to a groupof trunks individually extending to the group of trunk line circuits, this group `including the trunk 460 extending to the trunk line circuit 400; to a group of trunks individually` extending to the group of toll line circuits, this group including the trunk 590 extending to the toll line circuit 500; and to a group of trunks` individually extending to the group of trunk circuits, this group including the `trunk 610 extending to the trunk circuit 600. Similarly, each of the selectors has access to the group of trunksindividually extending to the group of outgoing trunk line circuits, this group including the trunk 305 extending to the outgoing trunk line circuit 300; to the group of trunks individually extending to the group of trunk line circuits, this group including the trunk 460 extending to` the trunk line circuit 400; to the groupof trunks individually extending to the group of toll line circuits, this group including` the trunk` `500 extending to the toll line circuit 500; and to a group of trunks individuallyextending to the local connectors in `the local switch train, this group including the trunk 945 extending to the local connector 94|.`

Each operator position at the switchboard'in the P. A. B. X 30 comprises position equipment including position apparatus, the position equipment provided at the first operator position 900 and at the last operator position 9|0 respectively including the rst position appara-tus H00 and the last position apparatus |000.`

The operator position 240 in the central office 20, asbest shown in Fig. 2, the operator position 260 1in the I. B. X 40, as best shown in Fig. 2,

and the ltoll operator position 250 inr the distant exchange 50, as best shown inl Fig. 2, are connected'and arranged in a conventional manner. Also the subscriber substations TI and T2 in the I. B. X 40, as best shown in Fig. 2, comprise conventional substation equipment; while the line circuits and trunk circuits vrespectively associated with the telephone lines and the trunks in the I. B. X 40, as best shown in Fig. 2, are connected and arranged in a conventional manner. Further the finder-connector links in the switch train in the I. B.` X 40, as best shown `in Fig. 2, are connected and arranged in a conventional manner; preferably, each of these links comprising a finder and a connector of the well-known Strowger type.

Preferably,v each of the outgoing trunk line 'circuits is identical to the outgoing trunk line circuit 360,shown in Fig. 3, which is connected and arranged in a conventional manner; while each of the incoming trunk line circuits is identical to the incoming trunk line circuit 300, shown in Fig. 3. The incoming trunk line circuit 300 comprises a repeater 340 and a number of relays, including a ring-up relay R3|0, a start relay R320 and a cutoff relay R330, connected and arranged in a manner more fully described subsequently.

Preferably, each of the trunk line circuits is identical to the trunk line circuit 40E), shown in Fig. 4, which comprisesa repeater 450 and a number of relays, including a control relay R410, a

start relay R420, a cutoff relay R430 and a line relay'R440, connected and arranged in arnanner more fully described subsequently.

Preferably, each of the toll line circuits is identical to the toll line circuit 500, shown in-Fig. 5, which comprises a repeater 50| and a number of relays, including a ring-off relay R510, a start relay R520, two control relays R530 and R560, a

cutoff relay R540, a ring-up relay R550, a` guard l relay R565, a timer relay R510, a hold relay vR515 and two count relays R580 and R585, connected and arranged in a manner more fully described subsequently.

Preferably, each of the trunk circuits is identical to the trunk circuit 600, shown inl Fig. 6, which comprises a repeater 660 and a number of relays, including a cutoff relay Rlll, a start relay R620, a line relay R030, a hold relay R640 and a recall relay R550, connected and arranged in a manner more fully described subsequently.

The subscriber substations T3 and T4 inthe P. A. B. X 30, as best shown in Fig. 9, comprise conventional substation equipment; while the line circuits associated with the telephone lines in the P. A. B. X 30, as best shown in Fig. .9,'are conpart 1 and. Fig. 7, partZ of the previously mentioned Voss and Crocker patent; while the selector of eachl switching link, such as the selector 82a, shown in Fig. e, of the switching link son( arranged in circumferentially spaced-apart relationship. Also the mechanism 1|0 includes a vertical control Wiper 1|1, capable of vertical movement, and an associated vertical control contact bank 1I8. The mechanism 110 is provided with .a vertical'magnet M1I8 for moving the wiper set thereof in the vertical direction, a` rotary magnetl M120 for moving the wiper set thereof in the rotary direction and a release magnet M122 for releasing the wiper set thereof and forcausing the wiper set thereof to be returned to its normal position. Finally the switching` mechanism 110 has a number of sets of switch springs S123 and S124 operatively associated therewith, which are controlled in accordance with the 'movements of the wiper set thereof, in a manner more fully described subsequently.

Further the finder 100 comprises a group of relays, including a switching relay R130, a transfer relay R140, a step relay R150, a start relay R155,a test relay R160 and a connect relay R110,

connected and arranged in a manner more fully described subsequently. Moreover, the nder'l has'individually associated therewith a link lis- I tening o r talk key K131i and a monitor key, not

shown', which are operative to associate the nder 100 with the cable 901 extending to the first operator kposition 900. Finally, a number of supervisory lamps L125 and L12@ are associated with the nder 100 for supervisory purposes.

Each operator position at the switchboard in the P. A. B. X 30, such as the rst operator position 900 and the last operator position SIU, shown in Fig. 9, comprises position equipment including a trunk circuit, a telephone instrument, key sender apparatus, ra number of control keys operative selectively to render different types of services over connections established at lthe operator position, and position apparatus.

nected and arranged in a conventional manner.

Further the local finder-selector links and the i local connectors in the local switch train in the P. A. B. X 30, as best shown in Fig. 9, are connected' and arranged in a conventional manner; preferably, each of the local finder-selector links comprising a local finder and a local selector, the local finders, ythe local selectors and the local connectors `being yof the well-known Strowger type- Preferably, each Vof the switching links 800,. 992, 9I2`, SIB, etc., shown in Figs. '1, 8 and 9, are identical, each of these switching links comprising a iinder and a selector. The finder of each switching link, such as the finder 100, shown in Figs; 7 vand 8, of the switching llink 800, is connectediand arranged in a manner substantially identical to that of the nder shown in Fig. 7,

More particularly, the trunk circuit, the telephone 'instrument and the control keys in the position equipment at each operator position are connected` and arranged in the manner of the trunk circuit, telephone instrument and control keys in the position equipment, shown in Fig. 21, part 1, Fig. 2l, part 2 and Fig. 21, part 3, of the previously mentioned Voss and Crocker patent; while the key sender apparatus in the position equipment at each operator position is connected and arranged'in the manner of the key sender apparatus in the vposition equipment, shown in Fig.' 22, part 1, Fig.` 22, part 2 and Fig. 23 of the previously mentioned Voss and Crocker patent. The first position apparatus H00 in the position equipment at the rst operator position 900 comprises, as best shown in Fig. 1l, a number of group lin-e keys, including the group line keys K||50 and Kll55, a number of individual line keys, including the individual line keys KNGU and KH65, a number of group line supervisory lamps, including the group line supervisory lamps Lllds and Li |49, a number kof individual line answer lamps, including the individual line answer lamps L||41` and L||45, and anumber i inclusive, provided with individually associated rotary `contact', banks ||||g` to |0inclusive, and a rotary magnet M|| 20 for driving the wipers noted. Finally, the rst position apparatus comprises a number of relays, including a start relay R||25 and a stop relay R||30. i i

Similarly, the last position apparatus `|00!) in the position equipment at the last operator position 9|0comprises, asbest shown in Fig. 10, a number of group line keys, including the group` linel keys K|050 and Kl055, a number of individual line keys, including the individual line keys K|060 and K|065, anumber` of group line supervisory lamps, including the group `line supervisory lamps L|048 and L|049, a number of individual line answer lamps, including the individual line answer lamps L|04`| and Ll045, and a number of individual line busy lamps, in-

cluding the individual line busy lamps L|046 and ;`L|044. Also the last position apparatus |000Ncomprises a marking switch |005 `of the well-known rotary type, including five rotary wipers` |0|| to |0|5`,` inclusive, provided with l individually associated rotary contact banks |0|6 to |0|0, inclusive, and a rotary magnet M|020 for driving the wipers noted. Finally, the last position apparatus `|000 comprises a number of relays, including a start relay R|025 and a stop relay Rl 030i Further it is noted that a group of line marke ing relays, including` the line i marking relays R`|040 and Rl |40, is commonly associated with themarking switches |005 and ||05 respectively included in the last position apparatus |000 and theiirst positionapparatus |00. Furthermore, in connection withthe last position apparatus |000 `and the iirst `position apparatus H00, it

is noted that the group line keys K|050 and K| |50 commonly correspond to the group of incoming trunk line circuits, including `the y incoming trunk linefcircuit 300; while the group line keys K|055 andK| |55 commonly correspond to the group of trunk circuits, including the `trunk circuit 600.` Similarly',` in' the last position apparatus A|000 and the iirst position apparatus' ||00, the individual line keys K|060 and K| |60 commonly ,correspond'to the individual toll linejcircuit 500 in the associated group of tollline circuits; `while the` individual line keys K|065 and Kl |65 commonly correspond to the individual trunk line cir- Cuit400 in the associated groupof trunk 'line circuits.`

better understanding of the'fconnection and arrangement of the `apparatus incorporated in theytelephone Vsystemvvill be `facilitated from` a consideration of the` detailedoperation of ,the various pieces ol?` apparatus incident to "the handling `of the various `toll and trunk calls at p the switchboard, as` will appear` hereinafter.

Local. call from a` subscriber substationin the P. A. B, X to the switchboard-'in the P. A. B. X

line circuit 936 individually associated with the telephone line 935 `ext-ending to the subscriber substation T4 to operate. Upon operating, the line circuit 936 initiates operation of one oi the local, finder-selector links, such as the local finder-selector link .940,in the local switch train,

whereupon the local finder-selector link 940 op-` subscriber substation T4 then dials a predeter` mined` digit thereat, thereby to cause the local `iinder-selector link 940 to operate and select an idle trunk in the associated `group of trunks extending to the group of trunk circuits. Assuming that the local lnder-selector link 940 operates to seize the trunk 680 extending to the trunk circuit 600when the trunk 680 is thus seized a circuit is completed for energizing in series the upper and lower windings of the line relay R630 in the trunk circuit 600, this circuit extending from ground by way of the lower winding of R630 and the i, winding 662 of the repeater 660 to the line conductor C682 of the trunk 680, and from i battery byway of the upper winding of the line relay R630 and the winding 66| of the repeater 660 to the line conductor C68| of the trunk 680, the line conductors C68| and C682 of the trunk 680 being connected by way of the local iinderselector link 940 to the telephone line 935. Accordingly, at this time, an operative connection is completed between the calling subscriber substation T4 and the repeater660. i

When thus energized theline relay R630 operates to complete, at the contacts 63|, an vobvious path for returning `ring-back tone current over the trunk 680, the local finder-selector link 940 and the telephone line 935 tothe calling subscriber substation T4, thereby to simulate at the subscriber substation T4 a ringing condition. Also the line relay `R630 completes, at the contacts 632, an obvious circuit for energizing the` trunk 680 as vbusy to the local` finder-selector links having access thereto, the `trunk 680 being previously `marked. for selection due to the completion of an obvious` path for applying battery `potential by way of the `resistor 6|'| to the con` y trol conductor`C683 thereof.,v Finally the hold vrelay R640 completes, at the contacts 645, a'n obf Vious `circuit for energizing the winding of the start relay R620, thereby to cause the latter relay to operate. 1Upon operating, the start relay R620 completes, at the contacts 622, an obvious path for applying battery potential by way of the upper Winding of the cutoi relay R6 I0 to the control i conductor C613 of the trunk 610, thereby tornark the rotary position of the trunk 610 in the main contact banks of the switching mechanisms 4of lthe finders having access thereto. Further `the Vstart relay R520 completes, at the contacts B25,

The call on the trunk 610rnay be answered at any operator kposition at the switchboard. For

example, the operatorV at the first operator positionl 900at the switchboard may `answer the call on the trunk 610 by rstselecting, in the event thishas not previously been done, an idle one of the switching links in the associated' group of switching links and then by operating the group line key KI |55 away from its normal position. In orderto select an idle one of the switching links in the group of switching links individually associated with the first operator position 900 Vthe operator thereat iirst determines that a given switching link is idle and then operates thetalk key of the finder thereof away from its normal position. For-example, assumingthat the switching link 800 is selected by the operator at the rst operatorrpos'ition 900 at this time, this switching link is indicated as being idle by the extinguished condition of the supervisorylamp L125. When the talk key K180 of the'rnd'er 100 of the switching link 800 is operated away Afrom its normalfposition there is completed, at the contactsd 18| thereof, :a circuit for energizing the upper winding of the connect relay R110, this circuit extending from ground in the position equip- `mentat the rst operator position 900 by way of the conductor C190 in the cable 90|, the contacts 18| ofthe talk key K180, the conductor C105 in the cable 90| and the upper winding of `R110 to battery. When thus energized the connect relay R110 operates to complete, at the contacts 118, a holding circuit for energizing the lower Winding thereof, this .circuit extending from ground in the position equipment atthe first operatorposition 900'byway vof the conductor C194 in the cable 90|, the contacts 186 of the talk key K180, the yconductor C105 in the cable 90|, the contacts 118 and the lower winding of R110 to battery. Also when this holding circuit is completed, apparatus in the position equipment at the first operator position 900 operates, thereby to cause ground potential to be removed from the conductor C190 in the cable 90| in order positively to prevent any of the otherv switching links inthe associated group of switching links from being connected to the cable 90|, as the switching link' 800 in this group of switching links is operatively connected to the cable 90| at this time. Further, at the contacts182,185 and 181, operative connections are completed to the position equipment at the first operator position 000 by way of the conductors C19|,.C192 and C195 in the cable 90| and the conductors CBII, C813 and C8|4 extending by way ofy the nder '|00` and the trunk 82| 4to the-selector 820. f r

l lAlso the connect relay R110 interrupts, at the contacts 1 13 and v116, the normally prepared connection between the wipers1|| and 1 I2 ofthe 'switching-mechanism 1| 0 'of-the finder v100and v'the conductors;8021andf8031extending by'way of trunks including theto thetrunk circuit 600 is C802 andl C803 extending by way ofthender 100 and the trunk 82| toA the` selector 820. Further theconnect yrelay-R110 prepares, at the contacts 110, a circuit traced hereinafter for energizing the winding of the test relay R150; interrupts, at the contacts 11 a point in a circuitv traced hereinafter for illuminating the supervisory lamp L125; prepares, at the contacts i12", al circuit traced' hereinafter for energizing the winding-` of the start relay R155; and prepares, at the contacts 113.', a path traced hereinafter for short-circuiting the` lower winding of the start relay R155.

Further the connect relay R110 completes, at the contacts `119, a further connection between the position equipment 'at the rst operator position 900 and the selector 820 by way of the conductor C101 inthe cable 90|, the contacts 119 and the conductor C801' extending by way of the finder 1,00 and the trunk 82| to the selector 82 0. At this i time the switching link 800 isl operatively associated with the cable 90| extendingto the rst operator position 900 andthe iinder 100 ofthe switching link 800 is in readiness' to be operated in order to route a call to the' iirst operator position 900.

When the operator at the iirstroperator position 000 operates the group line key K|| away from its normal position there is completed, at the contacts H51 thereof, an' obvious path for applying ground potential to the marking'conductor C|016 inthe cable"|090. yThis application ofv groundl potential to the marking conductor C|1010 in the cable |090 marks the vertical level inthe vertical control contact` banks of the switchingA mechanisms of the' finders of the switching links, wherein the trunk 610 extending Y l terminated. Also, at the contactsvr ||56jof the'group line key K||55, there is completed an obvious path for applying groundV potentiall toV they start j conductor C|018 in the cable |09 extending to the first operator posi-tion 900, which ground potential is forwarded by wayy of` the position equipmentV at' the rst operatory position 900 to the start conductor C|018 in the cable 90|: Thisf application of l ground potential to the'start ,conductor C|018v in the cable completes the previously mentioned circuit for energizing the upper winding of the ystart relay R155, this circuit extendingfrom the grounded start conductor C1018' in the cable 90| by way of the contacts 112","the set of switch springs S124- and the upper winding of R155 to battery. When thus energized the start `relay R operates tov complete, at the contacts 155, an obviousfpoint in multiple with the set of switch springs S124 `in thepreviously traced circuit for Yenergizing the'upper'windingI thereof', vto complete, at the contacts V158, an obvious circuit for illuminating the supervisory lamp L125, thereby to indicate tothe operator` atY the rst operator position 900: thatthe switching .link 800. is busy at, this time; Alsothe start relay R155 com- 'pletes; at thefcontacts 151'an obviousV holding circuitfo'r energizing the lower winding ofthe `switching relay R130 being of the polarized type.

Further the start relay 4,R155 completes, at the `contacts 151, a circuit for energizing the vertical' magnet M118, this` circuit extending from ground by wayofthe `contacts 151, 131, 152 and 145 `and the vertical magnet M118 ,to battery. When thus energized the vertical magnet M118 operates `to drive the 4wiper set of theswitching mechanism 110 one step in the vertical direction and to complete, at the contacts119, an obvious circuit for energizing the winding; of the step relay R150, thereby to `cause the latter relay to operate. Upon operating, the step relay R150 interrupts, at the contacts 152, the previously traced circuit for `energizing `the. vertical magnet M118 and prepares, atthe contacts 151, a

`test circuit traced hereinafter `for energizing the lower Winding of the transfer relay R140.

The vertical magnetM118 thenrestores to interrupt, at the contacts 119, the previously mentioned circuit for energizing the winding of the Step relay R150thereby to cause the latter relay `to restore. Uponrestoring, the step relay R150 interrupts, atthe contacts 151, a point in the previously mentioned test circuit for energizing the lower Winding ofthe transfer., relay R140 and recompletes, at the contacts 152, the previously traced circuit for energizing the vertical magnet M118. Accordingly, the vertical magnet M118 yand the step relay R150 interact in the manner described above, thereby to cause the wiper set of the mechanism 110 to` be driven step by step in the vertical direction until thevertical control wiper111 engages a contact in the associated vertical control contact bank 118 having ground l potential thereon.

In the present example, the vertical magnet M118 is energized intermittently six times, whereupon thevertical control wiper 111 engages the` C1016 havingground. potential thereon,'where- L fil) upon the previously mentioned test circuit for v energizing the lower winding of the transfer relay R140 is completed.' This circuit extends from the grounded marking conductor C1016 by way of the rvertical Ycontrol wiper 111 and engaged contact in the associated vertical `control contact bank 118, the contacts 143, the lower winding of R140, the contacts 151 and 145 and'thevertical magnet M118 to battery. When this series circuit is completed the vertical magnet M118 remains tacts 151, 131 and 142 and the upper winding of R140 to battery. Further the transfer relay R140 f interrupts, at the contacts `143,` the previously `traced series circuit for energizing the lower winding of the transfer relay R140 and the vertical magnet M118, thereby to cause the vertical magnet M118 to restore. Finally, the transfer relay R140 interrupts, at the contacts 145, a further point in the previously traced circuit for energizingthe .verticalmagnet M118 and prepares,l at the contacts 144, a circuit traced hereinafter for energizing the rotary magnet M120. Upon restoring, the vertical magnet M118 interrupts, at the contacts 119, the previously mentioned circuit for energizing the winding of the step relay R150, thereby to cause `the latter relay to restore. i

Upon restoring, the step relay R150 interrupts, at the contacts 151, a further point inthe previously traced series circuit .for energizing the lower winding of the transfer relay R140 and the vertical magnet M118 and completes, atthe contacts 152, the previously mentioned circuit for energizing the rotary magnet M120. This `circuit extends from ground by way of thev contacts 151, 131, 152 and 144 and the rotary magnet M120 to battery. When thusenergized the rotary magnet M120 operates to drive the wiper l .1 rotary magnet M120, thereby to cause the rotary magnet M120 to restore. Accordingly, the rotary magnetvM120' and the step relay R150 interact in the above-described manner, thereby to cause thewiper set of the switching mechanism to be driven step by step in the rotary direction until the control wiper 113` of the wiper set of theswitching mechanism 110 engages the contact in the associated contact set terminating the controlconductor C613 of the trunk 610; whereupon a circuit is completed for energizing in series the upper winding lof the switching relay R130 in the finder 100 and the upper winding of the cutoff relay R610 in the trunk circuit 600. This circuit extends from ground by way of the contacts 151, the upper winding of R130, the

contacts 162, the control wiper 113 of the switching mechanism 110,` the control conductor C613 of the trunk 610, the contacts 622 and the upper winding of R610 to battery. When this series circuit is completed the switching relay R130 operates exceedingly fast, thereby to interrupt, at the ycontacts 131, a further point in the previously traced circuit for energizing the rotary magnet M in order pOsitively to prevent further operation of the switching mechanism 110.

Also the switching relay R`completes, at the ftending from ground by way of the contacts 151 f `and and the intermediate winding of R130 to battery. Further the switchingrelay R130 completes, at the contacts 136, an obvious path for` short-circuiting the upper winding thereof, i

thereby to decrease the series resistance of the previously traced. circuit for energizing the upper winding of the cutoff relay R610, whereupon the latter relay is operated.` Upon operating, the lcutoff relay R610 completes, at the contacts 613, a holding circuit forenergizing the lower winding thereof, this circuit extending. from ground by way of the contacts 645 and `613 and the lower winding of R610'to battery. Further the cutoff relay R610 completesat the contacts 612, a multiple point in the previously traced circuit for energizing the upper winding thereof, interrupts, at the contacts 614, the initial path for applying battery potential to the control conductor C683 of the trunk 680 yand interrupts, at the contacts 611, the previously mentioned path Vthe calling subscriber substation T4, thereby to indicate to` thel subscriber thereat that the call has been answered at the switchboard in. the. P. A.. B. X 36. Finally,` the cutoff relay R616 interrupts, at the contacts 645, the previously traced multiple circuits for illuminating the group line supervisory lamps L|649,.L.|:|4'9, etc., at the various operator positions at the switchboard in order to indicate. to the operators thereat that the call on thetrunk in the. group of trunks, including the trunk 616,` has been answered at one ofthe operator positions at the switchboard. Further the switching relay R136 completes, at the contacts 138, a holding circuit for energizing the lower winding of theY start relay R155, this. circuit extending from ground by' way of the contacts 138 and 159", the lower winding of R155 and the resistor 121 to battery. Finally the switching relay R136 completes, at the con.- tacts 13| and 132, lan operative connection between the position equipment at the first operator f position 966 and the repeater 666 in the trunk circuit 666', thereby operatively to connect the first operator position-966 at the switchboard to the calling subscriber substationuT4.' More particularly, the position equipment at the. first operator position 966 isy connectedfby Wayr of the line conductors C162 and, C164 in the cable 96|, the contacts 112 and 115 and the contacts 13| and 132 to the line wipers 1|| and 1|2` of theV switching mechanism 1I6. Further this connection extends from the line wiper 'HI of the switching mechanism 1|6. by way iof they line conductor C61| of the trunk 61.6, the winding 663 of the repeater 666, the contacts 642 and 644, the winding 664 ofthe repeater 666 and the line conductor C612 of the trunk 616 to the line wiper 1|'2 of the switching mechanism 1|6.. .Also the windings 663, 664 and the windings 66|, 662 of the repeater 666 are inductively coupled, the windings 66| and 662 `of the repeater 666 being included in the previously traced loop circuit extending from the repeater 666. by way of the trunk 666,` the local finder-selector linkl 946 and thetelephone line 935 to the calling subscriber substation T4. Hence, at this time, an operative connection is completed between the calling subscriber substation T4 andthe iirst operator position 966 at the switchboard in the P. A. B. X 36, whereupon the operator at the first operator position 966jis advisedv concerning the extension of the call, and then extends` the call in a manner more fully explained hereinafter.

After the operator at the first operator position 966 answers the call she'returns the group line key K||55 back to its normal position,

vthereby to interrupt, at the contacts H51 thereof, the previously mentioned path for applying ground potential to the marking conductor C| 616 in the Icable |696 in order to remove g the marking from the corresponding contacts the completedholdingcircuitv for energizing the lowerv winding. thereof.

In View'y of. thef foregoing explanation of the mode of operationfof the nder 106 of the switching link 8661 in. thev group of switching links associated with: the firstoperator position 966 to seize the. trunk 616, it will be understood thatthe finder 963 of the' switching link 962 in this group of switching links is operative in a similar manner to nd the trunk 616. In.' other words, .the operator. at the` first operator position 966 may answer the., call on the trunk 616 vby utilizing any one of the switchinglinks'in the associated group of switching links merely by operating the link key of the4 nder of the selected switching link in combination with. ther group line key KI |55, in the manner previously explained. .After the operator at the first operator position 966' answers theV call on the trunk 6.16 and receives the information concerning the Aextension of the call'sheloperates the key sender apparatus. in the position equipment at the first operator position 966, thereby to control the operation` of the selector of the selected switching link. More particularly, assuming that the call on the trunk 616 is answered at the first operator position. 966l by utilizing the switching link 866, the selector 826is controlled in order to seize onen-fthe trunks accessible thereto, after which the' call is extended by way of the seized trunk to its destination. After extending the call to its destination the operator at the rst operator position 966 returnsthe ltalk key K186 of the lnder 166' of the switching link 866 back to its normal position, thereby to interrupt, at the contacts 186 thereof, the previously traced holding circuit for energizing the lower winding of the connect relay R116 and to interrupt, at the contacts 182, 185 and 181, the previously traced connections between the various conductorsv in the cable 96| and the various conductors extending by way of the finder 166 and the trunk 62| to the selector 826. The connect relay R116 then restores to interrupt, at the contacts 11|, 114 and 112, 115, the previously traced connections between the finder 166 and the selector 826 and the position equipment at the first operator position 966. Also the connect relay R116 completes, at the contacts 113 and 116, a direct connection between the finder 166 and the selector 826, thereby to complete an established connection, including the calling subscriber substation T4, the telephone line 935, the l local finder-selector link 946, the trunk 686, the -trunk circuit 666, the vtrunk 616 and the switching link 866 independent of the rst operator position 966; Further the connect relay R116 completes, at the contacts 11|', an obvious multipley circuit forl illuminating the supervisory lamp L125 and interrupts, at the contacts 113', a rfurther point in the previously mentioned path for short-circuiting the lower winding of the start relay R155. Further it is noted that, at the contacts 184 of the talk key K186 of the finder of the switching link 866, there is prepared a circuit traced hereinafter for illuminating. the supervisory lamp L126. f

The supervision and release of the established connection, including the switching link 866, is primarily under the control of the operator at the first operator position 966 and is. effected in the manner explained in the previously mentioned Voss and Crocker patent,

Moreparticularly, when a release operation is performedfat thecalling subscriber substation T4 `the localnder-selector link 940 is released* and the line circuit 936 is controlled, thereby to mark the telephone line 935 extending to the subscriber substation T4 as idle to the local connectors having access thereto. When the local finder-selector link 940 is released the previously traced circuit `for energizing the upper and lower` windings of the line relay R630 in the trunk circuit 600 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the line relay R530 completes, at the contacts 633, `a cir.- cuit for energizing'the lower winding of the recall relay R650, this circuit extending from ground by way of thelcontacts 624 and 633 `and the lower.` winding of R650 to battery. `When thus energized the recall relay R650 operates to complete, 'at the contacts 65|, a holding circuit for energizing the upper winding thereof and forilluminating the "supervisory lamp L126, this circuit extending from ground by way of the contacts 623, the upperfwinding of R650, the contacts 65|, thecontrol conductor C614 of the trunk 610, the controlwiper 11|4 of the switching mechanism 1|0, the conductors C804 and C8|3 in the finder 100, the contacts 184 ofthe talk key25 K180lof the iinder 100 and the supervisory lamp L126 to battery, the illumination of the supervisory lamp L126 indicates to the operator at the rstoperator position 900 that theestablished connection routed by way of the switching link 800 has beenreleased; l i

Also the line'relay R630 interrupts, at the contacts632, the `previously mentioned circuit for energizing the` winding of the hold relay R640,

therebytocause the latter relay to restore short,`

lythereafter, the hold relay R640 being of the slow-to-release type. Upon restoring, the hold relay R640 interrupts, at the contacts' 642 and 644, the previously mentioned direct connection between the windings 663 and 6640i the repeater 650, completes, at the contacts`643, an obvious path for applying battery potential by way of the resistor 6|6 to the line conductor C612 of the trunk 610 and completes, at the contacts 64|, an obvious path for `applying ground potential to the line conductor C|i1|` of the `trunk 610, the

application of ground and battery potentials to the; line conductors C61| and C612 of the trunk i 610 being utilized for supervisory purposes.` Further the hold relay R640 interrupts, at the con-` tacts 645, the previously traced multipl-e circuit for energizing the winding of the start relay R620 and the lower winding `ofthe cutoi relay RSIU, thereby `to cause the start relay R620 to restore shortly thereafter, the latter relay being ofthe slow-to-releas-e type. oi relay R6|0-1remains in its operated position due to the completed circuit` for energizing the upper `winding thereof. Upon restoring, the startrelay R620 interrupts, at the contacts 62| and `623, the previously mentioned paths for applying` battery and ground potentials to the line conductors C612 andV C61| of the trunk 610. Also the start relay R620 interrupts, at the` contacts 624, the previously traced circuit for energizing the lower winding of the recall relay R650 and interrupts, at the contacts 623, the previously traced holding circuit `for energizing the upper Winding of the recall relay R650thereby to cause the recall relay R650 to restore.

The; operator at the first operator` position 900 then operates the `talk key E180 of the nder 100 away from its normal position, thereby to cause `reoizeration of the connect relay R110 in However, the cuti the nder 100, in the manner previously explained. Upon reoperating, the connect relay R110 again connects the position equipment at the rst operator position 900 to the switching link 800, thereby to enable the operator at the rst operator position 900 to release the switching link 800.

In order to release the switching link 800 the operator at the rst operator position 900 controls the position equipment thereat, thereby to cause ground potential to be applied to the release conductor C108 in the cable 96|. This ap,- plication of ground potential to the release conductor C108 in the cable 90| completes a path 151 for` short-circuiting the lower winding of the start relay R155, this path extending from the grounded release conductor C108 in the cable 90| by way of the contacts 113', the lower winding of R155 and the contacts 159 and 138 toground. When the lower winding of the start relay R155 is thus short-circuited the latter relay restores. At this point it is noted that, when the wiper set of the switching mechanism 1|0 of the finder 100 isldriven one step in the vertical. direction,`

thesets of switch springs S123and S124 arerespectively actuated into engagement and disengagement. When the set of switch springs S123 is actuated into engagement av circuit traced hereinafter is prepared for energizing the release 30,A magnet M122; and when the set of switch springs S124 isactuated into disengagement the pref viously traced original circuit for renergizing the upper winding of the start relay R155 is interrupted. Accordingly, upon restoring, rthe start Lrelay R155 interrupts, at the` contacts 159, the previously traced path for short-circuitin'g` the lower winding thereof and completes, at the contacts 156, the previously `mentioned circuit for energizing the release magnet M122, the lastmymentioned circuit extending from ground by way of the contact 156, the setof switch springs S123 and the release magnet M122 to battery. `When thus energized the release magnet M122 operates to release the wiper set of the Aswitching mech-v A anism 1 |0, whereupon the wiper set of the switching mechanism 1 |0 is returned to its normal position. Also upon restoring, the` start relay R155 interrupts, at` the contacts 151, the previously traced holding circuit for energizing the upper walwinding of the transfer relayR'and the previously traced holding circuit for energizing the intermediate switching relay R130, thereby to cause the `latter relays to restore. wiper set of the switching mechanism 1|0 is re-v turned to its normal position the sets of switch into disengagement and engagement. When the set of switch springs S123 is actuated into `disengagement the previously traced circuit for en- 6ofergizing the release magnet M122 is interrupted, l

leased in order to indicate that the switching link Y 800 is idle at this time. Also, the release of the 'mlselector 820 is under the control of the operator i at theJ nrst operator position 900, and is effected in the manner explained in the` previously mentioned Voss and Crocker patent. When the selector 820 is released the previously mentioned 'lr/alternative circuit for illuminating the supere l When the springs S123 and-S124 are respectively actuated` `operator position 9|0. 'at the last operator position 9|0 the operator visory lamp L125 is interrupted, as previously explained. Y

The operator at the rst operator position 000 then returns the talk key X180 of the finder 100 'of the switching link B00 back to its normal position, thereby to'interrupt, at the contacts 100 thereof, the previously traced holding circuit for energizing` the lower winding of the connect relay R110, whereupon the latter relay restores.' At this time, both the nder 100 and the selector 820 of the switching link 800 are completely released and the switching link 000 is available for further use.

When the finder 100 of the switching link 800 is released the previously traced circuit for energizing the upper winding of the cutoff relay R||0 in the trunk circuit 000 is interrupted, thereby to cause the latter relay to'restore. Upon restoring; the cutoi relay RBI 0 recompletes, at the contacts 6|4, the previously mentioned path for applying battery potential by way of the resistor 6|1 to the control conductor C083 of the trunk 680 in order to mark the trunk 680 as idle to the local nder-selector links havingaccess thereto.

At this time, the apparatus utilized in the established connection between the calling subscriber substation T4 and the iirst operator position `900 at the switchboard is completely released and available for further use.y

Similarly, it will be understood that an operator at any other operator position at the switchboard in the P. A. B. X 30 may answer thev call on the trunk 010. IFor example, the operator at the last operator position 9|0 may answer the call on the trunk 610 by operating the group line key..K|055 away from its normal position aft-er selecting one of the switching links in the associated group. More particularly, when the operator at the lastV operator position 9 0 operates the group line key KI 055 away from its normal position there is completed, at the contacts |051 thereof, an obvious path for applying ground potential to the marking conductorC|016 in the cable |090, thereby to complete a path substantially identical to that previously traced for marking the vertical level in the contact banksofthe switching mechanisms of the finders of the switching links wherein the trunk 010 is terminated. Also, at the contacts |056 of the group line key K|055, there is completed an obvious path for applying ground potential to the start conductor C|010 in the cable |002 extending to the position equipment at the last operator position 9|0.` This application of ground potential to the start conductor C|010 in the cable` in the manner previously explained, whereupon an operative connection is completed between the calling subscriber substation T4 and the last After the call is answered thereat returns the group line key K|055 to its normal position, thereby to interrupt, at the contacts |051 andY |050, respectively, the previously mentioned paths for applying ground potential `to the marking conductor C|016 in the cable |090 CaZl from the central ooe to the P. B. X

In order to extend a call from the central oilice 20 to the switchboard in the P. A. B. X 30, the operator at the operator position 240 in ther central oilice 20 rst selects an idle trunk line in the group of trunk lines extending from the central oflice 20 to the P. A. B. X 30, such as the trunk line 205, and then operates the apparatus at the operator position 240, thereby to cause ringing current to be projected over the trunkV l-line V205. The projection of ringing current over the trunk line 205 completes a circuit for energizing the upper rwinding of the ring-up relay R3|0 in the incoming trunk line circuit 300, this circuit extending from the line conductor C206- o-f the trunk line 205 by way of the contacts 33|, the condenser 343, the contacts 3|| and the upper winding of R3|0 tothe line conductor C201 of the trunk line 205, the line conductors rC206 and'C201 of the trunk line 205 having ringing :voltage impressed therebetween. When thus energized the ring-up relay R3|0 operates to cornplete, at the contacts 3|2, a holding circuit for energizing in series the lower winding thereof and the lower Winding vof the start relay R320,

l this circuit extending from ground by way of the lower winding of R3l0, the contacts 3|2 and 335 and the lower winding' of R320 to battery. When this holding circuit is completed the ring-up relay R3|0 remains in its operated position while the start relay R320 operates. `Also the ring-up relay R3|0 interrupts, at the contacts 3||, the previously traced original circuit for energizing the upper winding thereof. Upon operating, the start relay R320 completes, at the contacts 323, a path for applying battery potential by way of the upper winding thereof to the control conductor C353 of the trunk 350, thereby to mark the rotary position of the trunk 350 in the main contact banks of theV switching' mechanisms of the iinders of the switching links having access thereto. vFurther the start relay R320 completes, at the contacts 324, an obvious path for applying ground potential to the control conductor C350 in the cable |090, thereby to complete obvi- `-lous multiple circuits for illuminating the group line supervisory lamps L|048, L| |48, etc., at the various operator positions at the switchboard in order to indicate to the operators thereat thatr l there is an incoming call from th'e central oice 20 to the P. A. B. X 30 on one of the trunks in the group of trunks, including the trunk 350.

This call may be answered at any one of the operator 'positions at the switchboard. For ex .,ample, in order to answer the call on'the trunk d350 at the rst operator position 900, the operator thereat operates the group line key KI |50 away from its normal position, thereby to complete, at the contacts |5I thereof, the previously ,traced path for applying ground potential to the start conductor C|018 in the cable |09| extending to the rst operator position 900 in order to initiate operation of the finder of the previously selected switching link in the associated group of -switching links. Also, at the contacts ||52 of the Vgroup line key KI |50, there is kcompleted an obvious path for applying ground potential to the marking conductor C|013 in the cable |000, thereby to mark the vertical level Yin the vertical control contact banks of the switching mechanisms of the finders Vof the switching links, wherein the trunk 350 extending to the incomin trunk line circuit 300 is terminated.

`The operation of the nder of the selected switching link in the group of switching links associated `with the first operator position 900 to seize the trunk 350 is substantially the same as that `previously explained; and after the trunk 350 isseized by the nder of the selected switching link the group line key KI |50 is returned to its normal position, thereby to interrupt, at the contacts and I |52 thereof, the previously traced path for applying ground potential respectively to the start conductor C|018 in the cable |09| 'and to the marking conductor C|013 in the cable |090.

When the finder of the selected link associated with the rst operator position 900 seizes the trunk 350 ground potential is applied to the control conductor C353 thereof, thereby to complete an obvious holding circuit for energizing the upper winding of the start relay R320 and to complete an obvious circuit for energizing the winding of the cutoff relay R330.A When thus'energized the cutoi relay R330 operates to complete, at the contacts 333, an obvious `holding circuit for energizing the winding thereof and to interrupt, 'at the contacts 335, the previouslytraced holding circuit for energizing the lower winding of the ring-up relay R3 |0 in series with the lower winding of the start relay R320, thereby to cause the ring-up relay R3|0 to restore. ringing voltage being impressed between the line conductors C206 and C201-of the trunk line 205 only momentarily by the operation of the apparatus at the operator position `240 in the central oilice 20. Also the cutoff relay R330 interrupts, at the contacts 336, the previously mentioned path for applying ground potential to the control conductor C356 in the cable |090, thereby to interrupt the previously traced multiple circuits for illuminating the group line supervisory lamps M1148,`

ators thereat that the call on the trunk in theV groupof trunks, including the trunk 350, has been answered at one of the operator positions at the switchboard. Finally the cutoff relay R330 completes, at the contacts 332,an operative connection between the operator position 240 in the central oflice 20 and the repeater 340 in the incoming trunk line circuit 300, this connection extending from the line conductor C206 of the trunk line 265 by way of the contacts 332, the windings 34| of the repeater 340 and th'e contacts 322 to the line conductor C201 of the trunk line 205, the line conductors C206 `and C201 of the trunk line 205 being operatively connected to the operator position 240 in the `central oice 20. Also it is noted that the windings 34| and 342 of the repeater 340 are inductively coupled, thereby to establish a connection `between the trunk line 205 extending from the operator position 240 in the central oiice 20 to the incoming trunk line circuit 300 and the trunk 350 seized by the finder of the switching link operatively associated with the rst operator position 900.

The subsequent extension and supervision of the connection attheiirst operator position 900 are the same as that previously explained. The release of the established connectionV is initiated by the operator at the operator position 240 in the central oice 20 and is accomplished when the operator at the operator position 240 operates the apparatus thereat, thereby to cause ringol current to be projected over the trunk line 205,. The projection of ring-off current over the lineconductor C205 completes an alternative circuit for energizing the upper winding of the ring-up relay R3|0, this circuit extending` from the line conductor C206 of the trunk line 205 by way of the contacts 32|, the condenser 343, the contacts 3|| and the upper winding of R3|0 to the line conductor C201 of the trunk line 205, the line conductor C206 and C201 of the trunk line V205 `having `ring-off potential impressed therebetween at the operator position 240 in the central omce 20. When thus energized the ringup relay R3|0 operates to complete, at the contacts 3|2, a holding circuit for energizing the lowerl winding thereof in series with the supervisory lamp L121, this circuit extending from ground by way of the winding of R3|0, the contacts 3|2 and 334., the control conductor C355 of the trunk 350, the control wiper 1|4 of the switching mechanism 1|0 of theiinder`100, the conductors C804 and C8|3 ofthe finder ,100, the contacts 184 of the talk key K180` and the supervisorylamp L126 to battery. The operator at the operator position 240 in the central oiice 20 thenoperates the apparatus thereat, thereby to in the manner previously explained.

When the switching mechanism 1|0 in the `finder of the switchin`glink`800 is released the previously traced multiple holding circuit for energizing the upper winding of` the start relay R320 and the winding of the cutofl relay R330 is interrupted, thereby to cause the start relay R320 to restore immediately 'and to cause the cutoff relay R330 to restore shortly thereafter, the cutoff relay R330 being of the slow-to-release type. Also when the switching mechanism 1|0 '1n the iinder 100 of the switching link 800 is released the previously traced holding circuit for energizing the lower winding of the ring-up relay R3 |0 is interrupted, thereby to cause `the latter relay to restore.` At this time the equipment utilized in the established connection between the operator position 240 in the central oice 20 and the` rst operator position 900 in the P. A. B. X 30 is completely released and available for further use Also it is noted that the operatorat any other operator position at the switchboard in the P. A B. X 30 may answer the call on the trunk 350. For example, the operator at the last operator position 9 0 may answer the call on the trunk 350 by operating the group line key K! 050 in combination with the talk key of the finder of one of the switching links in the group of switching links individually associated with the last operator position 9|0.

line key K|050 is operated away from its normal More particularly, the group position, thereby to complete, at the contacts 

